This invention relates to devices for connecting multiple bore conduit sections that are buried in the ground to a manhole.
With the increasing use of transmission lines, such as telephone and telegraph cables, computer data lines and cable television, as well as public protestations against above ground transmission towers, underground burial of cables has become the expedient used to provide a path for such cables. The use of buried conduit sections to provide cable passages not only overcomes public dissatisfaction with above ground installations, but also provides an economical way of expanding capacity without a great increase in capital costs required by erecting new transmission towers or gaining access to new rights of way, because conduit sections with excess capacity can be initially installed. Cable conduits that have been proposed in the past include those disclosed in commonly assigned U.S. Pat. Nos. 3,545,493 and 3,792,878, and in my copending, commonly assigned U.S. Pat. Application Ser. No. 403,248 filed Oct. 3, 1973.
Underground conduits are frequently connected to manholes which provide predetermined points for convenient access to the cables in the conduits. In the past, portions of manhole walls have often had to be knocked out to provide an opening for a conduit section, and it has not always been possible to create a water-tight seal between the conduit and the manhole wall.
One recurring problem is connecting conduits to manhole walls in the difficulty of connecting polyolefinic materials, such as conduit to a concrete manhole wall, due to the dissimilarity of the materials. Additionally, due to the confined nature of the working area, it is difficult to make a connection by using extraneous fasteners and connecting devices.
There is often loose fill adjacent to the manhole wall, which results in the ground settling beneath the conduit. Void areas can thus occur beneath the conduit, resulting in a substantial decrease in ground bearing support of the conduit. With increasing depths of burial and increasing conduit widths, greater pressure is presented on the conduit, particularly in areas adjacent to manholes. It is therefore important to have a high-strength connection between the conduit and the manhole wall.